1. Field of the Invention
The present invention relates generally to a method and apparatus for pyrolyzing of waste materials. More particularly, the invention concerns a method and apparatus for pyrolyzing a wide variety of substances in either a liquid, sludge, solid or mixed state.
2. Discussion of the Prior Art
Various methods and apparatus for pyrolyzing waste materials have been suggested in the past. Typically pyrolytic decomposition of waste materials is carried out in an atmosphere which is kept substantially oxygen free by exclusion of air. As a general rule, the waste is pyrolyzed in a closed retort maintained at elevated temperatures in the range of between 400.degree. C. and 800.degree. C.
In recent years considerable effort has been devoted to perfecting the design of large, highly efficient, relatively polution free pyrolysis equipment for use in the pyrolysis of various types of waste materials including domestic and industrial waste. For example, in U.S. Pat. No. 4,084,521 issued to Herbold, et al, a method and apparatus for the pyrolysis of old tires and other vulcanized waste products of rubber or plastic is disclosed. In the relatively early U.S. Pat. No. 3,020,212 issued to Lantz, a pyrolytic refuse converter for use in pyrolyzong domestic and industrial waste is disclosed.
One of the drawbacks of most of the prior art methods and apparatus for pyrolysis of waste products resides in the inability of the apparatus to efficiently process waste products materials in the liquid form or waste products embodying large amounts of moisture. When such materials are introduced into the pyrolysis chamber, substantial energy is required to maintain the elevated temperature required to efficiently pyrolyze the materials. A particular problem encountered in processing such materials concerns the start up of the pyrolyis process.
One of the by-products of the decomposition of most domestic and industrial waste is methane gas. Accordingly, once proper start-up is accomplished, the pyrolysis process can be sustained by burning the methane gases produced by the process. However, start-up must be accomplished using an outside energy source such as natural gas or the like. Experience has shown that unless the waste products are properly treated before being introduced into the pyrolysis apparatus, the time required to achieve a self-sustaining reaction is inordinately long and, on occasion, the production of by-product methane gas remains insufficient to sustain the reaction without the addition of natural gases or other sources of energy. This inability to achieve a self-sustaining reaction can be extremely costly. Further, unless the waste materials within the retort are thoroughly decomposed, polution levels can become inordinately high.
As will be better understood from the description which follows, the method and apparatus of the present invention solves many of the drawbacks of prior art pyrolysis techniques by providing an apparatus wherein the waste material is pre-treated through the use of microwaves to preprocess the waste material prior to its introduction into the pyrolysis chamber. By carefully pre-processing the waste products start-up time is minimized so that the methane and other volatile gases which are produced as a result of the decomposition of the waste materials can be used relatively soon in the process to sustain the reaction.
In starting up the pyrolysis process, prior art apparatus typically used natural gas as the source of energy to initially ignite the waste material and pyrolyze it to a point that the production of methane gas was sufficient to sustain the pyrolysis reaction. This approach is costly and time consuming. In remote locations where natural gas is not available even more expensive propane or the like must be used. In the apparatus of the present invention, pre-ignition is uniquely is accomplished using energy derived from a high-powered, apparatus for light amplification by simulated emission of radiation commonly known as an industrial "laser". This device efficiently raises the temperature of the waste material to ignition temperatures and rapidly brings the apparatus to an operating point wherein the methane gas produced from the waste material being paralyzed is more than sufficient to sustain the pyrolysis reaction. In point of fact, additional volatile gases, over and above that necessary to sustain the reaction, is quickly produced. This excess produced gas can be used for a variety of purposes such as powering electrical generation equipment for the generation of electricity for use on or off the premises.
Basically the process of the present invention involves a introduction of waste material from a holding tank by means of a suitable material moving means such as a pumping apparatus. The pumping apparatus provides for a constant flow of waste material into the pre-processing or dehydrating apparatus wherein the material is subjected to microwaves produced by a large microwave generator. Following pre-drying of the waste, the waste material is then metered into the pyrolysis retort where it is controllably conveyed longitudinally of the retort by means such as a rotating, high temperature alloy helical screw.
Initial ignition of the pre-processed waste material is accomplished in a hypoxic, or oxygen-free, chamber of the retort by means of the high powered, industrial scale ruby or CO2 laser. High energy laser radiation is directed at the predried waste material and is continued until sufficient volatile gases are produced from the decomposition of the waste material to sustain the reaction. The produced gases are continuously collected and then burned in one or more gas burners disposed within the retort proximate the pyrolysis chambers.
The process material, which will not gasify, is conveyed to the exit end of the retort and dropped through an airlock onto a secondary conveyer which transports it to a storage bin. As previously mentioned, the excess volatile gases produced by the apparatus are available for power generation through a variety of systems. For example, if a plant where the pyrolysis retort is located has a boiler, furnace or after-burner, the methane gas can be directly fired into the after-burner and the resultant heat energy produced used to reduce the need for other conventional sources. Because the by-product carbon char produced by the pyrolytic converter is inert, it can be readily disposed of in an ordinary landfill or can be salvaged for a variety of other commercial purposes.